State detecting circuit, key-press detector, and musical instrument

Abstract

A state detecting circuit has a first switch circuit connected to a first selection line and a second switch circuit connected to a second selection line. The first switch circuit includes two switches, and performs an arithmetic operation of ON/OFF states of the switches and a selection signal. Thus, since one switch circuit performs an arithmetic operation using ON/OFF states of the two switches, the number of selection lines and the number of parts can be reduced.

The invention claimed is: 
     
       1. A state detecting circuit comprising:
 a plurality of switch circuits, each of the plurality of switch circuits comprising at least one switch which switches between an ON state and an OFF state in response to a change in a physical amount which is a target of detection, each of the plurality of switch circuits configured to output a state signal which changes according to an ON/OFF state of the switch included in the switch circuit itself, 
 wherein the plurality of the switch circuits include one or a plurality of three-state switch circuit comprising two switches in which thresholds of the physical amount at which the switch switches between the ON state and the OFF state are different from each other, configured to invert the state signal when the physical amount exceeds a smaller one of the thresholds of the two switches, and further configured to invert the state signal when the physical amount exceeds a larger one of the thresholds of the two switches, 
 wherein the plurality of switch circuits include at least one two-state switch circuit having a threshold between the thresholds of the two switches of the three-state switch circuit, and configured to invert the state signal when the physical amount exceeds the threshold. 
 
     
     
       2. The state detecting circuit according to  claim 1 ,
 wherein the plurality of switch circuits include the plurality of three-state switch circuits, and the switch of the two-state switch circuit has, assuming that the thresholds of the physical amount at which the respective switches of the plurality of switch circuits switch between the ON state and the OFF state are sorted in ascending order, a threshold in a next order of a largest threshold among the smaller thresholds among the thresholds of the respective two switches of the plurality of three-state switch circuits. 
 
     
     
       3. The state detecting circuit according to  claim 1 ,
 wherein the plurality of switch circuits include the plurality of three-state switch circuits, sections between the thresholds of the respective two switches of the plurality of three-state switch circuits have an inclusion relation, and a switch of the two-state switch circuit has a threshold inside an innermost section among the sections having the inclusion relation. 
 
     
     
       4. The state detecting circuit according to  claim 1 ,
 wherein the plurality of switch circuits include the plurality of three-state switch circuits, and in the plurality of the three-state switch circuits, a section between the thresholds of the two switches of at least one of the three-state switch circuits overlaps with a section between the thresholds of the two switches of another one of the three-state switch circuits, and a switch of the two-state switch circuit has a threshold between a largest threshold and a smallest threshold among the thresholds of the respective switches of the plurality of three-state switch circuits. 
 
     
     
       5. The state detecting circuit according to  claim 1 ,
 wherein the plurality of switch circuits include, as the plurality of three-state switch circuits, two three-state switch circuits in which sections between the thresholds of the two switches of the respective three-state switch circuits do not overlap with each other, and has, as the at least one two-state switch circuit, a two-state switch circuit having a switch with a threshold between thresholds of the two switches of one of the two three-state switch circuits and a two-state switch circuit having a switch with a threshold between thresholds of the two switches of another one of the two three-state switch circuits. 
 
     
     
       6. The state detecting circuit according to  claim 1 ,
 wherein one of the two switches of the three-state switch circuit is a key-on switch, and the other of the two switches is a key-off switch. 
 
     
     
       7. A key-press detector for detecting key press depth of a key on a keyboard, comprising:
 a state detecting circuit comprising: 
 a plurality of switch circuits, each of the plurality of switch circuits comprising at least one switch which switches between an ON state and an OFF state in response to a change in a physical amount which is a target of detection, each of the plurality of switch circuits configured to output a state signal which changes according to an ON/OFF state of the switch included in the switch circuit itself, 
 wherein the plurality of the switch circuits include one or a plurality of three-state switch circuit comprising two switches in which thresholds of the physical amount at which the switch switches between the ON state and the OFF state are different from each other, configured to invert the state signal when the physical amount exceeds a smaller one of the thresholds of the two switches, and further configured to invert the state signal when the physical amount exceeds a larger one of the thresholds of the two switches, and 
 wherein the switches comprised of the switch circuits are provided in a lower part of the key such that each of the switches comprised of the switch circuits switches when the key is pressed down to an amount corresponding to the threshold of the switch. 
 
     
     
       8. A musical instrument comprising a keyboard and the key-press detectors according to  claim 7 ,
 wherein the key-press detectors are provided to correspond to respective keys of the keyboard for detecting key press depth of the corresponding key.